Quote Originally Posted by Maggie View Post
We just tested our water and the TC is very low, while TA and pH are really high...how can it be so alkaline AND have such high pH (over 8.5) simultaneously? And it says there is almost NO calcium...but I am afraid to add some because it is already so alkaline and basic...what is going on?
What is going on is your water is out of balance...nothing really strange. Easy to fix. A normal part of water maintenance.

High TA (level of bicarbonate in the water) will lead to high pH because there is a lot of carbonation in the water and the constant aeration found in hot tubs causes CO2 to gas off. Outgassing of CO2 is the primary cause of pH rise in hot tubs and pools. The cure is to lower the TA. You lower TA by adding acid. This also lowers pH. You then aerate which causes pH to rise again. You then add more acid, aerate, and repeat this process until the TA is on target. See the sticky in the forum on how to lower TA for full instructions. It's pretty easy in a hot tub because to aerate just turn on all the jets and bubblers and open the venturis ( and turn on the blower if you have one). High TA and high pH tend to go hand in hand, BTW! That is normal.
If the chlorine is low you need to add more. Period. End of story. It's really that simple! You want to be testing for Free Chlorine (good chlorine that is available to sanitize), btw. Total Chlorine the total of Free Chlorine and Combined Chloramines (spent or bad chlorine) so it is not really what you want to be testing for.
As far as the calcium goes...if the tub is acrylic (most stand alone hot tubs are) you don't need to worry about low calcium. Ideally you want it around 130-150 ppm to minimize foaming but it really does not need to be any higher than that and many people run it lower. If the spa is plaster or aggregate then you do need to maintain enough calcium to maintain a proper calcium saturation index to protect the plaster finish.
How are you testing the water. If you are using strips then your measurements are very possibly bogus. The fact that you stated the pH is over 8.5 leads me to believe you are using strips. Get a decent test kit. The one recommended is the Taylor K-2006. It will make maintaining your spa MUCH easer.
Finally, you did not give us any test result numbers. A full set of test results (not done with strips) that include free chlorine, combined chlorine (or total chlorine so the combined chlorine can be calculated), pH, TA, CH, and CYA (cyanuric acid or stabilizer.....this is a needed test for any chlorine pool or spa!) would tell us better what might be going on in your water! Also, what is your primary chlorine source (dichlor, bleach or liquid chlorine, lithium hypochlorine, calcium hypochlorite) and how many gallons is the spa?